Diversity Combining in a Single-Input-Multiple-Output Molecular Communication System

Molecular communication (MC) can enable nano-scale devices to communicate with each other using molecules as information carriers. To enhance the performance of MC, receiver-devices with multiple receiving ports can be utilized to form single-input multiple-output (SIMO) and multiple-input multiple-output (MIMO) communication links. The receiver ports are analogous to antennas in wireless communication. This paper considers a diffusion-based MC SIMO system with a point transmitter and one receiver system with many receiving ports (RxPs). We first characterize the joint channel between the transmitter and RxPs. We then present the optimal maximum-a-posteriori (MAP) decoding for this system when all ports can share complete information and a central device soft-combines the individual signal values to decode the signal. We then consider a Poisson channel approximation for the channel and show that weighted linear combining is an optimal decoding scheme with weights depending on average channel values. We also study a symmetric SIMO system and investigate the decoding error probability and diversity order for various soft and hard combining schemes.